Improve email notifications status messages

Add "Failed with output", and shorten "Failed with non-zero exit code"
to "Failed".
Omit the system type if it's part of the job name
Always show the links related to the build product.
reproduce.tt: Set revCount for hg repos

The revision counting changes depending on which revision is cloned
initially, so clone the default branch first and then checkout the
required revision to match hydra's revCount.

Signed-off-by: Shea Levy <shea@shealevy.com>
hydra-module.nix: find sendmail in /var/setuid-wrappers
hydra-module.nix: strip trailing whitspace
release.nix: disable tests run in virtual machine environment

My build machine cannot run qemu-kvm. I can probably run those tests
with standard qemu, but first I need to figure out how.